The invention relates to calculator or digital data processing systems, and particularly to a technique for displaying data in such systems.
Electronic calculator systems of the type having all of the main electronic functions within a single large scale integrated (LSI) semiconductor chip, or a small number of chips, are described in the following prior applications or patents assigned to Texas Instruments Incorporated: U.S. Pat. No. 3,819,921, by Kilby et al., for "Miniature Electronic Calculator", based on an application originally filed Sept. 29, 1967; Ser. No. 163,565, filed July 19, 1971, by Boone and Cochran, for "Variable Function Programmed Calculator" (now Ser. No. 420,999, filed Dec. 3, 1973); Ser. No. 400,473, filed Sept. 24, 1973, by Bryant for "Digit Mask Logic In Electronic Calculator Chip"; Ser. No. 400,437, filed Sept. 24, 1973, by Vandierendonck, Fisher and Hartsell for "Electronic Calculator With Display And Keyboard Scanning"; Ser. No. 397,060, filed Sept. 13, 1973, by Cochran and Grant, for "Multi-Chip Calculator System"; Ser. No. 525,236, filed Nov. 19, 1974, by Raymond and Caudel, for "Electronic Calculator or Digital Processor Chip With Multiple Code Combinations of Display And Keyboard Scan Outputs"; and others.
These prior inventions have made possible vast reductions in cost and size, and increases in functions, in electronic calculators. Many millions of such calculators have been produced. The efforts to reduce manufacturing costs and increase the functions available to the user are continuing. Particularly, it is desirable to provide a basic chip structure that is quite versatile and can be used for many different types of calculators and similar digital processing equipment. This permits a single manufacturing facility to produce large quantities of the same devices, differing only in a single mask change, to produce dozens of different variations, while still maintaining large volume cost advantages.
Although the MOS/LSI calculator system as referred to above incorporated on one or two chips all of the computational circuits of the calculator, including data registers, arithmetic unit, a ROM for containing the program, and all of the control circuits, input/output decoders, and the like, it was still necessary to have certain external devices on a printed circuit board to provide a completed calculator. That is, the MOS/LSI package, along with a display and a keyboard, did not alone provide a calculator. Initially, hand-held, battery operated "one-chip" calculators required, in addition to the MOS/LSI chip, several external circuits for power supply, clock generators, and digit and segment drivers. Subsequent developments have made it possible to eliminate the external clock generator circuits by placing these on the chip itself. By using improved MOS processes, it is possible to eliminate or minimize the external power supply circuitry; if the MOS logic will be operated at low voltage, then it can be driven directly from batteries. The digit and segment drivers have heretofore been necessary, however, because the electrical specifications for drive voltage and current have been such that MOS/LSI components were not suited to drive LED's directly.
It is the primary object of this invention to provide a calculator system or the like wherein no components external to an MOS/LSI chip are needed, other than a display and a keyboard. Another object is to provide improved display drive circuitry for an electronic calculator or the like. Another object is to provide a more versatile output multiplexing arrangement for a calculator or digital processor. A further object is to provide an improved technique for display and keyboard scanning in a calculator or the like.